Conversion of paraffins to gasoline

ABSTRACT

An improved two-step process for the conversion of lower molecular weight paraffins, the process comprising contacting in a first step a C 2  -C 10  alkane-rich feedstock with a siliceous zeolite catalyst in a primary fluidized bed reaction zone under high temperature dehydrogenation conditions to obtain an intermediate product comprising oligomerizble olefinic hydrocarbons and aromatics; and then contacting in a second step the intermediate product with a siliceous zeolite catalyst in a secondary fluidized bed reaction zone under low temperature oligomerization conditions to obtain a final product comprising gasoline boiling range aliphatic and aromatic hydrocarbons.

BACKGROUND OF THE INVENTION

In a modern petroleum refinery several process units generatehydrocarbon byproducts of low commercial value. Side streams comprisinglower molecular weight paraffins are generally low in value and oftenburned as a source of fuel.

Efforts to upgrade hydrocarbon streams containing C₂ -C₁₀ paraffins haveincluded contacting the paraffins under high severity dehydrocyclizationconditions with a crystalline shape selective medium pore siliceous acidcatalyst in a fluidized bed reaction zone to obtain aromatichydrocarbons such as benzene, toluene and isomeric xylenes (BTX). Suchan operation provides a convenient one-step route for producing anaromatics-rich gasoline with a relatively high octane number.

U.S. Pat. No. 3,827,968 (Givens et al) discloses a two-stage operationwherein a mixed feed containing paraffins and olefins is upgraded in theabsence of added hydrogen to a highly aromatic gasoline product. In afirst stage oligomerization reaction, olefins are upgraded to highermolecular weight liquid hydrocarbons under relatively mild conditionswith a catalyst having the structure of ZSM-5. In a second stage, saidliquid hydrocarbons are converted to an aromatic product. A gas phasehighly paraffinic stream is withdrawn as by-product from the firststage.

SUMMARY OF THE INVENTION

The invention integrates a dehydrocyclization process operated at mildconditions with an oligomerization-aromatization process to efficientlyconvert C₂ -C₁₀ paraffins to highly aromatic and olefinic gasolinehaving a high octane rating. In a preferred process of the invention, adual fluidized bed vertical column reactor comprising a lower transportriser reaction zone and an upper turbulent flow reaction zone, bothzones containing fluidized catalyst comprising acid medium poremetallosilicate zeolite, is maintained for contacting the paraffinicfeed with catalyst. The feed enters the dual column reactor at the lowertransport riser reaction zone under high temperature dehydrogenationconditions to substantially prevent cracking reactions. An intermediateproduct comprising dehydrogentated hydrocarbons and aromatics leaves thelower zone and enters the upper turbulent zone operated at conditions toenhance oligomerization. A final product comprising gasoline boilingrange hydrocarbons is obtained.

Accordingly, it is a primary object of this invention to provide aprocess for converting lower molecular weight alkanes to gasoline bydehydrogentaion of C₂ -C₁₀ paraffins to form olefins, feeding theolefins to an oligomerization zone, and converting the olefins to avaluable gasoline product in the oligomerization zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow sheet showing the overall operation of theinvention.

FIG. 2 is a diagram of a preferred process of the invention with dualreaction zones enclosed in a single reactor tower.

FIG. 3 is a graph of gasoline selectivities versus operational spacevelocity.

FIG. 4 is a graph of C₅ + gasoline octane-BBL versus operational spacevelocity.

DETAILED DESCRIPTION OF THE INVENTION

It is known in the art that lower molecular weight alkanes can beefficiently upgraded to valuable hydrocarbon products by contacting thealkanes under high severity dehydrocyclization conditions with an acidcatalyst having the structure of ZSM-5. A number of chemical reactions,such as dehydrogenation, oligomerization, alkylation, and aromatization,are occurring at such operating conditions. In this one-step process,paraffinic feedstock is converted to aromatic hydrocarbons comprisingBTX.

An improved process has been discovered for converting C₂ -C₁₀ paraffinsto gasoline boiling range hydrocarbon product without the use of highseverity dehydrocyclization conditions and with the concomitant increasein volumetric yield and octane-BBL rating of the product.

In FIG. 1, the overall process of the invention is shown in flow diagramform. A C₂ -C₁₀ paraffinic stream is fed via line 1 to a dehydrogenationzone 2 to obtain an effluent rich in a oligomerizable hydrocarbons. Theeffluent is withdrawn via passage 3 and enters separation zone 12 wherean aromatics-rich stream is optionally withdrawn by means 4. The streamrich in aromatics can be added to the final gasoline product obtainedvia line 9.

An intermediate product comprising olefinic hydrocarbons either with orwithout aromatics made in the first stage 2 enters oligomerization zone22 by means of line 5. Optionally, a co-feed comprising C₂ + olefin-richstream can be added as by means 6 to oligomerization zone 22 to convertolefins to gasoline.

A final product comprising gasoline boiling range hydrocarbons andunreacted paraffins enters separation zone 32 by means of inlet 7. AC₅ + gasoline product is withdrawn by means of outlet 9. Unreacted C₂-C₆ component such as paraffins and olefins are collected and recycledvia line 8 to the dehydrogenation zone 2.

Referring to FIG. 2, a feedstream rich in C₂ -C₄ alkanes is injected viapassage 1 into a dual reactor vertical column 30. In a preferredexample, C₂ -C₄ alkanes are contacted with a ZSM-5 catalyst in atransport riser reaction zone 10 which comprises the lower portion ofvertical reactor 30 under dehydrogenation conditions comprising atemperature of about 537° C. to 895° C. and a pressure of about 50 to2000 kPa and a WHSV of 1 to 1000 to covert less than about 80 wt. % ofC₂ -C₄ alkanes to intermediate olefinic product.

The intermediate product comprising oligomerizable olefins, aromatics,and unreacted paraffins can be contacted directly with a catalyst havingthe structure of ZSM-5 in a turbulent flow fluidized bed reaction zone20 which comprises the upper portion of vertical reactor 30 to convertgreater than about 80 wt % intermediate olefins. Operating conditionsfor the turbulent flow reaction zone are based on typical MOG (MobilOlefins to Gasoline) technology and comprise temperatures of about 215°C. to 535° C. and pressures of about 50 to 2000 kPa and a WHSV of about0.1-10. The catalyst, which preferably comprises ZSM-5, may have an acidcracking value of about 2 to 35, preferably about 5-10. Thermal balancecan be maintained by employing a heat exchange line 2 containing steamor preheated feedstock. Optionally, a co-feed comprising C₂ + alkenescan be introduced by means of line 8 to the upper turbulentoligomerization zone. This stream may also be used as a quench tomaintain thermal balance in the fluid bed without using exchange line 2.

A product comprising C₅ + gasoline range hydrocarbons and unreactedalkanes is withdrawn via line 3 and enters recovery zone 40 where agasoline stream is recovered as by line 9 and an overhead hydrogen richC₂ - stream is withdrawn as by line 11.

Catalyst is withdrawn via line 4 and enters regeneration zone 50 foroxidative rejuvenation with an oxygen-containing gas such as airentering as by means 6. Freshly regenerated catalyst is combined withparaffinic feed via line 5 for contacting in the dehydrogenation zone10. A portion of the regenerated catalyst can be sent directly toreaction zone 20 via line 14. Flue gas is withdrawn from catalystregeneration zone via means 7.

Enhancement of overall process economy can be achieved by employing thesame catalyst in both the lower transport zone 10 and the upperturbulent zone 20. As catalyst is partially deactivated it istransported from the lower zone to the upper zone where it functions asan olefins oligomerization and aromatization catalyst.

The catalysts preferred for use herein include crystallinealuminosilicate zeolites having a silica-to-alumina ration of at least12, a Constraint Index of about 1 to 12 and acid cracking activity ofabout 16-200. Representative of suitable zeolites are ZSM-5, ZSM-11,ZSM-12, ZSM-23, and ZSM-35. ZSM-5 is disclosed and claimed in U.S. Pat.No. 3,702,886 and U.S. Pat. No. Re. 29,948; ZSM-11 is disclosed andclaimed in U.S. Pat. No. 3,709,979. Also see U.S. Pat. Nos. 3,832,449for ZSM-12; 4,076,842 for ZSM-23; 4,016,245 for ZSM-35. The disclosuresof the above patents are incorporated herein by reference. A suitableshape selective catalyst is a HZSM-5 zeolite with alumina binder in theform of cylindrical extrudates. Other catalysts which may be usedinclude a variety of medium pore (˜5 to 8 Angstroms) siliceousmaterials, such as borosilicates, ferrosilicates and/oraluminosilicates, disclosed in U.S. Pat. Nos. 4,414,143 and 4,417,088,incorporated herein by reference.

It is not necessary to employ only medium pore metallosilicate zeolitecatalysts in the reaction zones. A large pore zeolite material can beused.

The medium pore shape selective aluminosilicate catalyst can containother materials, such as P, Ga, Sn, Re, Zn, Pt, and Cu, which areincorporated in the catalyst by known procedures such as ion exchange,etc.

Referring to FIG. 3, selectively for both C₄ + gasoline and C₅ +gasoline is plotted against the operational space velocity in adehydrocyclization reaction employing a saturated lower aliphaticfeedstock. Conditions of temperature and pressure are maintained asconstants. Conventional gasoline-from-paraffins operations employpreferably a maximum LHSV of about 2.5, while the process of the presentinvention preferably employs a LHSV of about 25. The present processincreases C₅ + gasoline selectively about 10% by volume based onfeedstock; and the C₄ + gasoline selectively is increased about 20% byvolume based on feedstock.

In FIG. 4 C₅ + gasoline octane-BBL is plotted against the liquid hourlyspaced velocity of a feedstock comprising saturated lower molecularweight hydrocarbons. In standard dehydrocyclization reactions, thepreferred maximum LHSV of paraffinic feedstock is about 2.5 hr.⁻¹ whichgives a product with C₅ + gasoline octane-BBL ratings of about 54.5(M+0) and about 60.5 (M+R/2). When the LHSV of the feedstock isincreased in accordance with the present process, C₅ + gasoline-BBLratings are increased significantly.

In the process for dehydrocyclization of a parafinic feedstockcomprising C₂ -C₁₀ alkanes in a primary fluidized bed reaction zone overa catalyst comprising crystalline medium pore acid siliceous zeoliteunder high severity conversion conditions of WHSV, temperature, andpressure to obtain an aromatic product comprising benzene, tolueneand/or xylenes, the improvement of the present invention comprisesoptimizing the operating severity by adjusting the space velocity andtemperature in the primary reaction zone to effect partial conversion ofthe paraffinic feedstock, thereby effectively dehydrogenating the C₂-C₁₀ alkanes to obtain an intermediate product comprising maximum lowerolefins plus aromatics, adding a secondary fluidized bed reaction zonein series with the primary reaction zone, the secondary reaction zonecontaining a catalyst comprising crystalline medium pore acid siliceouszeolite; and contacting the intermediate product in the secondaryfluidized bed reaction zone over the siliceous catalyst underoligomerization conditions to obtain a final product comprising C₅ +gasoline boiling range aliphatic and aromatic hydrocarbons andunconverted alkanes.

In the primary reaction zone less than about 75 wt. % of C₂ -C₁₀ alkaneis converted to intermediate product; and in the secondary reaction zonegreater than about 90 wt. % of intermediate lower olefinic product isconverted to C₅ + gasoline boiling range aliphatic and aromatichydrocarbons.

To increase output of gasoline product, it is desirable to introduce anauxiliary feedstock comprising oligomerizable lower olefins to thesecondary reaction zone, withdrawing final product from the secondaryfluidized bed reaction zone and separating the product to obtain a highoctane gasoline. The unconverted alkanes separated from final productare recycled to the primary fluidized bed reaction zone for furtherconversion.

The C₂ -C₁₀ alkane feedstock preferably comprises propane. Othersuitable feedstocks are ethane, butane, pentane, and hexane in any oftheir isomeric forms, either alone or in admixture with one another.Another useful feed is the reformer paraffins separated in an extractionunit such as Udex. Other preferred feeds include the saturated gas plantLPG as the paraffinic feedstock and the USGP LPG with or without theethene fraction as the olefinic feedstock.

In the alternative, the lower molecular weight oligomerizable olefinscan be added to the intermediate product prior to contact in thesecondary fluidized bed reaction zone. Examples of lower molecularweight oligomerizable olefins are ethene, propene, the isomeric butenes,pentenes, and hexenes. The olefin can be added individually or inmixtures.

The crystalline medium pore siliceous catalyst in the primary reactionzone preferably comprises a zeolite having the structure of ZSM-5. Mostpreferably, the catalyst comprises HZSM-5.

In the secondary reaction zone, the crystalline medium pore siliceouscatalyst preferably comprises a zeolite having the structure of ZSM-5.Most preferably, the catalyst comprises HZSM-5.

The high severity reaction conditions in the primary fluidized bedreaction zone comprise a temperature of about 537° C., a pressure ofabout 50 to 2000 kPa, and a catalyst acid cracking value of about 5 to50. The oligomerization conditions in the secondary fluidized bedreaction zone comprise a temperature of about 215° C. to 535° C., apressure of about 50 to 2000 kPa, and a catalyst acid cracking value ofabout 2 to 10.

In a preferred embodiment, the present invention relates to a processfor the conversion of C₂ -C₁₀ alkanes to olefinic and aromatichydrocarbons boiling in the gasoline range comprising: contacting afeedstock comprising at least one C₂ -C₁₀ alkane with a catalystcomprising crystalline medium pore acid siliceous zeolite in a primaryfluidized bed reaction zone under high temperature dehydrogenationconditions to substantially prevent cracking reactions to obtain anintermediate product comprising dehydrogenated hydrocarbons andaromatics; and contacting the intermediate product with a catalystcomprising crystalline medium pore acid siliceous zeolite in a secondaryfluidized bed reaction zone under lower temperature oligomerizationconditions to obtain a final product comprising gasoline boiling rangehydrocarbons and unreacted C₂ -C₁₀ alkane.

The following example is intended to illustrate the benefits of thepresent two-stage process.

EXAMPLE

A paraffinic hydrocarbon feedstock comprising FCC light gasoline iscontacted under dehydrocyclization conditions with a shape selectiveacidic metallosilicate zeolite catalyst. The liquid hourly spacevelocity of the feedstock is increased in stage from 2.5 hr.⁻¹ to 75hr.⁻¹. At increasing LHSV, total aromatics production decreases andproduction of reactive olefins is increased as represented in Table 1below. Operation of a dehydrocyclization reaction at relatively highLHSV produces an olefinic hydrocarbon product which is then oligomerizedin a second stage to obtain high quality gasoline. In addition, gas makeis significantly reduced reaction heat input requirements are reduced,catalyst make-up rate is reduced, benzene concentration in the finalgasoline product is reduced, hydrogen purity is increased, and productrecovery is less expensive.

                  TABLE 1                                                         ______________________________________                                        LHSV       2.5     5.0    12.5  25.0 37.5  75.0                               ______________________________________                                        (Wt. %)                                                                       H.sub.2    1.9     1.9    1.9   1.3  1.0   0.5                                methane    10.8    4.3    3.0   1.7  1.4   0.8                                ethene     2.0     6.5    8.1   8.6  10.0  9.5                                ethane     8.2     7.2    4.9   3.5  2.3   1.7                                propene    1.5     7.6    10.2  13.5 15.7  19.2                               propane    9.5     11.7   11.6  11.3 10.4  8.8                                butanes    1.5     6.9    7.7   13.3 14.8  14.4                               pentanes   4.3     3.2    3.8   7.8  10.4  13.5                               total aromatics                                                                          60.7    51.1   48.7  39.4 34.3  26.9                               benzene    14.5    12.5   8.4   5.9  5.5   3.1                                toluene    30.5    25.1   22.3  17.9 15.3  14.2                               xylenes    12.1    10.8   13.2  11.8 10.3  6.5                                C.sub.9+  aromatics                                                                      3.6     2.7    4.8   3.8  3.2   3.1                                ______________________________________                                    

Table 2 shows the product selectively when the two-stage alkaneconversion reaction is compared with the conventional one-stagedehydrocyclization reaction. The product selectivity is shown in poundsper hour (Lbs/hr) and barrels per day (BPD).

                                      TABLE 2                                     __________________________________________________________________________              One-Stage Reaction                                                                      Two-Stage Reaction                                        LHSV      2.5       2.5   5     12.5  25    37.5  75                          __________________________________________________________________________    Lbs/hr                                                                        C.sub.4   150       120   520   640   880   1010  1120                        disomerized C.sub.5+ *                                                                  430       740   1630  2000  2990  3560  4240                        Benzene   1440      1440  1240  840   590   550   330                         Toluene   3030      3030  2490  2240  1780  1520  1490                        Xylene    1200      1200  1070  1320  1170  1030  680                         C.sub.9+  360       360   270   480   380   320   330                         Total C.sub.5+                                                                          6460      6770  6700  6880  6910  6980  7070                        Total C.sub.4+                                                                          6610      6890  7220  7520  7790  7990  8190                        BPD                                                                           C.sub.4   17.08     14.63 61.63 75.83 104.04                                                                              118.89                                                                              132.45                      disomerized C.sub.5+ *                                                                  39.91     68.68 151.29                                                                              185.63                                                                              277.52                                                                              330.42                                                                              393.54                      Benzene   111.51    111.51                                                                              96.02 65.05 45.69 42.59 25.55                       Toluene   238.04    238.04                                                                              195.62                                                                              175.98                                                                              139.84                                                                              119.41                                                                              117.06                      Xylene    94.48     94.48 84.24 103.93                                                                              92.12 81.10 53.54                       C.sub.9+  28.67     28.67 21.51 38.23 30.27 25.49 26.28                       Total C.sub.5+                                                                          512.62    541.39                                                                              548.68                                                                              568.82                                                                              585.43                                                                              599.01                                                                              615.97                      Total C.sub.4+                                                                          529.70    556.02                                                                              610.31                                                                              644.65                                                                              689.47                                                                              717.90                                                                              748.42                      C.sub.5+ (R + O)                                                                        119.2     118.0 114.2 115.2 111.5 109.1 107.0                       C.sub.5+ (M + O)                                                                        106.4     105.1 101.2 101.5 97.7  95.4  93.4                        C.sub.5+ (ROAD)                                                                         112.8     111.6 107.7 108.3 104.6 102.3 100.2                       R + O (BBLS/D)                                                                          61103     63879 62664 65502 65254 65366 65927                       M + O (BBLS/D)                                                                          54517     56908 55553 57709 57198 57169 57529                       ROAD (BBLS/D)                                                                           57810     60394 59108 61606 61226 61267 61728                       __________________________________________________________________________     *Includes non aromatic C.sub.5+ made in the first stage reaction plus         total C.sub.5+ made in the second stage reaction.                        

Composition of C₅ + gasoline product is shown in a comparative fashionin Table 3 for both the conventional one-stage dehydrocyclizationreaction and the two-stage alkane conversion reaction of the presentinvention.

                                      TABLE 3                                     __________________________________________________________________________                One-Stage Reaction                                                                      Two-Stage Reaction                                      LHSV        2.5       2.5 5   12.5                                                                              25  37.5                                                                              75                                  __________________________________________________________________________    disomerized C.sub.5+, Vol %                                                               7.79      12.69                                                                             27.57                                                                             32.63                                                                             47.40                                                                             55.16                                                                             63.89                               Benzene, Vol %                                                                            21.75     20.60                                                                             17.50                                                                             11.44                                                                             7.80                                                                              7.11                                                                              4.15                                Toluene, Vol %                                                                            46.44     43.97                                                                             35.65                                                                             30.94                                                                             23.89                                                                             19.94                                                                             19.00                               Xylene, Vol %                                                                             18.43     17.45                                                                             15.35                                                                             18.27                                                                             15.74                                                                             13.54                                                                             8.69                                C.sub.9+, Vol %                                                                           5.59      5.30                                                                              3.92                                                                              6.72                                                                              5.17                                                                              4.25                                                                              4.27                                Total       100.00    100.00                                                                            100.00                                                                            100.00                                                                            100.00                                                                            100.00                                                                            100.00                              __________________________________________________________________________

While the invention has been described by specific examples andembodiments, there is no intent to limit the inventive concept except asset forth in the following claims.

What we claim is:
 1. A continuous process for conversion of C₂ -C₄alkanes to aromatic rich hydrocarbons boiling in the gasoline rangecomprising:maintaining a dual vertical column reactor comprising a lowertransport riser reaction zone and an upper turbulent fluidized bedreaction zone, both zones containing fluidized catalyst comprising acidmedium pore metallosilicate zeolite; contacting a feedstock comprisingat least one C₂ -C₄ alkane with fluidized catalyst in the lowertransport zone under high temperature dehydrogenation conditions todehydrogenate the feedstock and substantially prevent cracking reactionsto obtain an intermediate product comprising dehydrogenated hydrocarbonsand aromatics; and contacting the intermediate hydrocarbon product withfluidized catalyst in the upper turbulent zone under lower temperatureoligomerization conditions to obtain a final product comprising C₅ +gasoline boiling range hydrocarbons.
 2. A process according to claim 1wherein the C₂ -C₄ alkane feedstock comprises propane, and the zeolitehas the structure of ZSM-5 zeolite.
 3. A process according to claim 1wherein an auxiliary feedstock comprising oligomerizable olefins isadded to the intermediate product for contact in the upper zone.
 4. Aprocess according to claim 1 wherein less than about 80 wt. % of C₂ -C₄alkane is converted to intermediate product in the lower transport zone.5. A process according to claim 1 wherein greater than about 80 wt. % ofdehydrogenated hydrocarbons converted to final product in the upperzone.
 6. A process according to claim 1 wherein unreacted C₂ -C₄components are separated from final product and recycled to the lowertransport zone for conversion.
 7. A process according to claim 1 whereinthe siliceous zeolite in both zones comprises HZSM-5.
 8. A processaccording to claim 1 wherein deactivated catalyst is withdrawn from theupper turbulent flow reaction zone and contacted with anoxygen-containing gas for regeneration.
 9. A process according to claim8 wherein regenerated catalyst is added to the lower transport riserreaction zone.
 10. A process according to claim 1 wherein reactionconditions in the lower transport zone comprise a temperature of about537° C. to 895° C, a WHSV of 1-1000, and a pressure of about 50 to 2000kPa.
 11. A process according to claim 1 wherein reaction conditions inthe upper turbulent zone comprise a WHSV of 0.1 to 10, temperature ofabout 215° C. to 535° C., and a pressure of about 50 to 2000 kPa.
 12. Aprocess according to claim 1 wherein the siliceous metallosilicate acidzeolite catalyst contained in the lower transport zone has an acidcracking value of about 5 to
 50. 13. A process according to claim 1wherein the siliceous metallosilicate acid zeolite catalyst contained inthe upper turbulent zone has an acid cracking value of about 2 to 10.14. A process according to claim 1 further comprising withdrawing thefinal product from the upper turbulent zone and separating the productto obtain a high octane gasoline.
 15. In a process fordehydrocyclization of a paraffinic feedstock comprising C₂ -C₁₀ alkanesin a primary fluidized bed reaction zone over a catalyst comprisingcrystalline medium pore acid siliceous zeolite under high severityconversion conditions of temperature and pressure to obtain an aromaticproduct comprising benzene, toluene and/or xylenes, the improvementcomprising:(a) optimizing the operating severity by adjusting the spacevelocity and temperature in the primary reaction zone to effect partialconversion of the paraffinic feedstock, thereby effectivelydehydrogenating the C₂ -C₁₀ alkanes to obtain an intermediate productcontaining maximum lower olefins and aromatics. (b) adding a secondaryfluidized bed reaction zone in series with the primary reaction zone,the secondary reaction zone containing a catalyst comprising crystallinemedium pore acid siliceous zeolite; and (c) contacting the intermediateproduct in the secondary fluidized bed reaction zone over the siliceouscatalyst under oligomerization conditions to obtain a final productcomprising C₅ + gasoline boiling range aliphatic and aromatichydrocarbons and unconverted alkanes.
 16. A process according to claim15 wherein the C₂ -C₁₀ alkane comprises propane, and the zeolitecatalyst in the primary and/or secondary reaction zone comprises azeolite having the structure of ZSM-5.
 17. A process according to claim15 wherein an auxiliary feedstock comprising oligomerizable lowerolefins is added to the secondary reaction zone.
 18. A process accordingto claim 15 wherein less than about 80 wt. % of C₂ -C₁₀ alkane isconverted to intermediate product.
 19. A process according to claim 15wherein greater than about 80 wt. % of intermediate lower olefinicproduct is converted to C₅ + gasoline boiling range aliphatic andaromatic hydrocarbons.
 20. A process according to claim 15 whereinunconverted alkanes are separated from final product and recycled to theprimary fluidized bed reaction zone.
 21. A process according to claim 15wherein the high severity reaction conditions in the primary fluidizedbed reaction zone comprise a WHSV of about 1-1000, a temperature ofabout 537° C. to 895° C., a pressure of about 50 to 2000 kPa, and acatalyst acid cracking value of about 5 to
 50. 22. A process accordingto claim 15 wherein the oligomerization conditions in the secondaryfluidized bed reaction zone comprise a WHSV of about 0.1-10, atemperature of about 215° C. to 535° C., a pressure of about 50 to 2000kPa, and a catalyst acid cracking value of about 2 to
 10. 23. A processaccording to claim 15 further comprising withdrawing final product fromthe secondary fluidized bed reaction zone and separating the product toobtain a high octane gasoline.
 24. A process for the conversion of C₂-C₁₀ alkanes to aromatic rich hydrocarbons boiling in the gasoline rangecomprising:contacting a feedstock comprising at least one C₂ -C₁₀ alkanewith a catalyst comprising crystalline medium pore acid siliceouszeolite in a primary fluidized bed reaction zone under high temperaturedehydrogenation conditions to substantially prevent cracking reactionsto obtain an intermediate product comprising aromatic and olefinichydrocarbons; and contacting the intermediate product with a catalystcomprising crystalline medium pore acid siliceous zeolite in a secondaryfluidized bed reaction zone under lower temperature oligomerizationconditions to obtain a final product comprising gasoline boiling rangehydrocarbons and unreacted C₂ -C₁₀ alkane.
 25. A process according toclaim 24 wherein the C₂ -C₁₀ alkane comprises propane.
 26. A processaccording to claim 24 wherein the crystalline medium pore acid siliceouszeolite in the primary and/or secondary reaction zones comprises azeolite having the structure of ZSM-5.
 27. A process according to claim24 wherein an auxiliary feedstock comprising lower molecular weightoligomerizable olefins is added to the intermediate product prior tocontact in the secondary fluidized bed reaction zone.
 28. A processaccording to claim 24 wherein less than about 80 wt. % of C₂ -C₁₀ alkaneis converted to intermediate product.
 29. A process according to claim24 wherein greater than about 80 wt. % of intermediate olefinichydrocarbons are converted to final product.
 30. A process according toclaim 24 wherein unreacted C₂ -C₁₀ alkane is separated from finalproduct and recycled to the primary fluidized bed reaction zone.
 31. Aprocess according to claim 24 wherein the high temperature bed reactionzone comprise a WHSV of about 1-1000, a temperature of about 537° C. to895° C., a pressure of about 50 to 2000 kPa, and a catalyst acidcracking value of about 5 to
 50. 32. A process according to claim 24wherein the lower temperature oligomerization conditions in thesecondary fluidized bed reaction zone comprise a WHSV of about 0.1-10, atemperature of about 215° C. to 535° C., a pressure of about 50 to 2000kPa, and a catalyst acid racking value of about 2 to
 10. 33. A processaccording to claim 26 wherein the catalyst comprises HZSM-5.
 34. Aprocess according to claim 26 wherein the zeolite having the structureof ZSM-5 contains a metal cation selected from the group consisting ofP, Ga, Sn, Re, Zn, Pt, and Cu.
 35. A process according to claim 24wherein an auxiliary feedstock comprising lower molecular weightoligomerizable olefins is added to the secondary fluidized bed reactionzone as a fluidized bed distributor while the intermediate product fromthe primary reaction zone is added to the secondary reaction zone at apoint above the auxiliary feedstock.
 36. A process according to claim 35wherein the intermediate product added to the secondary reaction zonecontains an amount of entrained catalyst particles from the primaryreaction zone.
 37. A process according to claim 35 wherein theintermediate product is separated from entrained catalyst particlesprior to addition to the secondary reaction zone.
 38. An apparatus forthe continuous conversion of C₂ -C₄ alkanes to aromatic richhydrocarbons boiling in the gasoline range comprising:a dual verticalcolumn reactor comprising a lower transport riser reaction zone and anupper turbulent fluidized bed reaction zone, both zone containingfluidized catalyst comprising acid medium pore metallosilicate zeolite;means for contacting a feedstock comprising at least one C₂ -C₄ alkanewith fluidized catalyst in the lower transport zone under hightemperature dehydrogenation conditions to dehydrogenate the feedstockand substantially prevent cracking reactions to obtain an intermediateproduct comprising dehydrogenated hydrocarbons and aromatics; and meansfor contacting the intermediate hydrocarbon product with fluidizedcatalyst in the upper turbulent zone under lower temperatureoligomerization conditions to obtain a final product comprising C₅ +gasoline boiling range hydrocarbons.
 39. An apparatus for the conversionof C₂ -C₁₀ alkanes to aromatic rich hydrocarbons boiling in the gasolinerange comprising:means for contacting a feedstock comprising at leastone C₂ -C₁₀ alkane with a catalyst comprising crystalline medium poreacid siliceous zeolite in a primary fluidized bed reaction zone underhigh temperature dehydrogenation conditions to substantially preventcracking reactions to obtain an intermediate product comprising aromaticand olefinic hydrocarbons; and means for contacting the intermediateproduct with a catalyst comprising crystalline medium pore acidsiliceous zeolite in a secondary fluidized bed reaction zone under lowertemperature oligomerization conditions to obtain a final productcomprising gasoline boiling range hydrocarbons and unreacted C₂ -C₁₀alkane.